guestfs_lstatlist, guestfs_lxattrlist: Reimplement to avoid protocol limits.

Note that the code to do this was already in virt-ls, so this is
change is mostly just moving the code into the core library.

TODO

@@ -565,6 +565,4 @@ with the non-daemon versions implemented using guestfs_upload and
 guestfs_download (and others).  This change should be transparent from
 the p.o.v of the API and ABI.
 
- - guestfs_lstatlist
- - guestfs_lxattrlist
  - guestfs_readlinklist